In many industries there is a need for an electric connector or switch capable of connecting an electric contact member to a metallic object without igniting combustible fluids which may surround the connector. For example, when explosive fuels, such as hydrocarbons, are pumped into or out of a metallic reservoir, such as a barge or truck tanker, the surrounding atmosphere is loaded with combustible fumes. It may happen that when a metallic object, external to such a reservoir, touches the reservoir there will be produced an arc that may ignite the explosive fumes.
Various attempts have been made to solve that problem. A method and system for protecting a barge is described in copending Patent Application Ser. No. 946,901, filed on Sept. 28, 1978, and assigned to the same assignee. The system for protecting the barge is illustrated in connection with the use of a metallic conduit for pumping hydrocarbon fluids into or out of the barge. The undesirable arcing can take place when the metallic conduit is connected to or disconnected from the barge.
The invention in said application involves connecting the barge to the earth through a barge-grounding cable, connecting the metallic conduit to the earth through a conduit-grounding cable, whereby a grounding circuit is established with a current source connected between the earth and the grounding cables.
The currents flowing through the grounding cables are being continuously monitored by an alarm circuit forming part of the grounding circuit in order to determine the presence and location of a broken cable or of an ineffective electric connection between the cable and the barge. The alarm circuit has suitable visual and audible warning devices which will indicate safe and dangerous operating conditions, as well as generally identify the location of faults.
As more fully explained in said application, the reason why arcing takes place when the metallic loading arms are connected to or disconnected from the barge is that both the barge and the loading arms are in a electrolytic circuit. When the loading arms are connected to the barge, electric current will flow because there is a potential difference therebetween, say on the order of 0.5 volts. Since the resistance in this electrolytic circuit is very small, a very large current can flow between the barge and the loading arms. This large current will produce arcing when the metallic loading arms first make contact with the barge.
As above-mentioned, the invention in said patent application relies on connecting a grounding cable to the barge. Such connection can be made through a C-clamp and an explosion-proof switch so that when arcing across the switch does occur, it will cause no damage.
The switch, in accordance with prior practice, must be contained within an explosion-proof housing. First, the C-clamp connects the grounding cable to the barge. Then the switch is turned ON. The resulting arcing, if any, produced between the contacts of the switch was completely contained within and confined to the inside of this explosion-proof housing.
Thus, the function of such a switch is to operate in combination with the C-clamp so as to allow the C-clamp to connect the grounding cable to the metallic body of the barge in such a manner that the arcing, if any there is produced, when the electric connection is established between the grounding cable and the barge, will be harmless to the explosive fumes in the immediate vicinity of the C-clamp and of the explosion-proof switch.
Thus, the propensity of the C-clamp to cause an explosion has been immobilized, in accordance with the prior art, by combining the C-clamp with an external explosion-proof switch.
It is an object of the present invention to provide an explosion-proof connector, in general, and a C-clamp, in particular, which does not require an external explosion-proof switch. Thus, the main difference between the prior art and the present invention resides in the elimination of the need for an explosion-proof switch externally of the C-clamp.
Thus, the expression "arcless connector" as used herein means a connector which can connect a metal object to an electric cable and which does not need an external explosion-proof switch. From the point of view of the explosive gases surrounding the connector of the present invention, it is as if the connector of the invention produced no arcing at all. The arcless connector and the inherent advantages thereof are illustrated by the novel structures of the embodiments of the invention.